Nucleic acids play a key role in cellular functions. Because chemical alterations in active nucleic acids by UV-, x-, and gamma-ray radiation produce mutagenic, lethal, and other biological effects, ultraviolet and radiation chemistry and biology of nucleic acids have been in the foreground of scientific research for the past three decades. Therefore, in order to understand the action of ultrasound on biological systems, studies on ultrasonic radiation of nucleic acids and their components are essential especially in considering the increasing clinical use of ultrasound. Our systematic investigation will continue to be conducted in a dual fashion: 1) the study of the sonochemical changes of nucleic acid bases, nucleosides, and nucleotides and polynucleotides at low levels of sonication (less than or equal to 5W/cm2, less than 30 min, 1 MHz) and 2) the examination of the inactivation of H. influenzae transforming DNA and of the degradation of SV40, phi x-174, and T7 DNA. The effects of various parameters such as temperature, concentration, sonic intensity, pH, ionic strength, dissolved inert gases, etc. will be examined. Dose-response studies, analyzed by high pressure liquid chromatography for the appearance of sonoproducts, the decrease in the UV absorbancy of the reactant, and, in addition, by radioactivity distributions of labelled compounds after sonication and chromatography. At the same time, the biological studies will emphasize on establishing the threshold conditions of inactivation of transforming DNA and of single and double-strand degradations of superhelical and various DNAs.